U.S. patent application number 10/718913 was filed with the patent office on 2004-06-03 for powered orthotic device.
Invention is credited to McBean, John M., Narendran, Kailas N..
Application Number | 20040106881 10/718913 |
Document ID | / |
Family ID | 32397104 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040106881 |
Kind Code |
A1 |
McBean, John M. ; et
al. |
June 3, 2004 |
Powered orthotic device
Abstract
A powered orthotic device, worn about a patient's elbow or other
joint, senses relatively low level signals in the vicinity of the
joint generated by a patient having spinal cord or other nerve
damage. In response to the relatively low level signals, the
powered orthotic device moves, causing the patient's joint to move
accordingly.
Inventors: |
McBean, John M.; (Boston,
MA) ; Narendran, Kailas N.; (Alston, MA) |
Correspondence
Address: |
DALY, CROWLEY & MOFFORD, LLP
SUITE 101
275 TURNPIKE STREET
CANTON
MA
02021-2310
US
|
Family ID: |
32397104 |
Appl. No.: |
10/718913 |
Filed: |
November 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60428196 |
Nov 21, 2002 |
|
|
|
Current U.S.
Class: |
601/5 ;
601/33 |
Current CPC
Class: |
A61B 5/389 20210101;
A61F 2/72 20130101; A61H 1/0277 20130101; A61H 2205/06 20130101;
A61B 5/4528 20130101 |
Class at
Publication: |
601/005 ;
601/033 |
International
Class: |
A61H 001/02 |
Claims
What is claimed is:
1. A powered orthotic device for augmenting a person's muscular
functionality comprising: a brace adapted to be coupled to a body
pair of the person and having a length such that the brace
traverses a joint of the person, said brace including at least one
strap for attaching the brace to the body part of the person;
sensing means, fixed in at least one of the at least one straps
such that when said strap is coupled to the body part said sensing
means is coupled to at least one muscle of the person and wherein
in response to the person attempting to move the body part said
sensing means senses a surface electromyographic (EMG) signal of
the muscles connected to the joint and determines a desired joint
torque from the EMG signal and provides a sensor signal in response
thereto; and an actuator coupled to receive the sensor signal from
said sensing means and in response to the sensor signal said
external actuator provides a force having a magnitude which is
proportional to a magnitude of the sensor signal provided by said
sensing means and wherein the ratio of power delivered by said
actuator to the mass of the actuator takes into account all of the
elements needed to generate the force.
2. The device of claim 1 further comprising: means for receiving
the sensor signal and for scaling the sensor signal by a variable
amount; and an active feedback control loop circuit coupled to
control the amount of force applied to the joint by said external
actuator.
3. The device of claim 2 wherein said active feedback control loop
circuit further comprises means for providing a measurement of
output torque to ensure an accurate application of force.
4. The device of claim 3 further comprising: a cable drive coupled
between said actuator and said brace such that in response to
movement of the actuator, said cable drive moves the brace.
5. The device of claim 4 further comprising a wheelchair wherein:
at least a portion of said cable drive system is coupled to said
wheel chair; and said actuator is disposed such that the mass of
said actuator is substantially supported by said wheelchair.
6. The device of claim 1 wherein said actuator corresponds to an
electric actuator.
7. The device of claim 1 wherein said actuator corresponds to a
hydraulic actuator which comprises a compressor and wherein the
ratio of power delivered by said actuator to the mass upon which
the actuator acts is selected to be above a predetermined threshold
level.
8. The device of claim 1 wherein said actuator corresponds to a
pneumatic actuator which comprises a compressor and wherein the
ratio of power delivered by said actuator to the mass upon which
the actuator acts is selected to be above a predetermined threshold
level.
9. A powered orthotic device for augmenting a person's muscular
functionality comprising: a brace adapted to be coupled to a body
part of the person and having a length such that the brace
traverses a joint of the person; sensing means coupled to at least
one muscle of the person wherein in response to the person
attempting to move the body part, said sensing means noninvasively
senses a desired muscular force of the person and provides a sensor
signal in response thereto; an external actuator coupled to receive
the sensor signal from said sensing means and in response to the
sensor signal said external actuator provides a force having a
magnitude which is proportional to a magnitude of the sensor signal
provided by said sensing means wherein the ratio of power delivered
by said actuator to the mass of the actuator takes into account all
of the elements needed to generate the force; a control means
coupled to said external actuator, said control means including
means for making a low impedance measurement of output torque and
for providing a feedback signal to said external actuator to ensure
an accurate application of the force provided by said external
actuator.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application No. 60/428,197 filed
Nov. 21, 2002.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
FIELD OF THE INVENTION
[0003] This invention relates generally to orthotic devices and
more particularly to a powered orthotic device worn by a person
about an existing limb or body part.
BACKGROUND OF THE INVENTION
[0004] Rehabilitation following severe neurological trauma, such as
spinal cord injury or stroke, is difficult, but has been shown to
provide useful results. Conventionally, physical therapy methods
are used for such rehabilitation. However, these methods are labor
intensive, often requiring one or more therapists to work with each
patient. Conventional physical therapy methods include repetitive
movement of a patient's limb or body part, with therapist
assistance, in an attempt to strengthen muscles and improve lost
muscle control associated with the limb or body part. This type of
therapy is most often performed in a hospital. When the patient can
effectively move the limb or body part so as to be able to care for
themselves the patient may be discharged from the hospital.
[0005] Robot aided therapies have been developed as a way of
cutting labor costs associated with rehabilitation. Conventional
robot-aided therapy includes repetitive movement of a patient's
limb or body part by means of a separate robot arm or the like, in
much the same way that a physical therapist would move the
patient's limb during conventional manual physical therapy. It has
been shown that patients treated daily with additional robot-aided
therapy during rehabilitation have improved motor activity at
hospital discharge. There is evidence that improved recovery can
result from more therapy, earlier therapy, and therapies that
incorporate highly repetitive movement training. However, current
robotic devices and therapies require the use of relatively large
and expensive robots, practically suitable only for inpatient
services at hospitals. Although the total labor cost may be reduced
with robotic therapies, the therapy is still performed while the
patient is an inpatient, still resulting in a relatively high
cost.
[0006] With both robotic and manual therapies, a patient's
progression thorough the therapy is essentially the same, i.e.,
they are subjected to a period of"rehabilitation" before being able
to accomplish activities of daily living. The patient subjected to
these therapies is generally not able to quickly return to normal
activities outside of the inpatient environment.
[0007] For example, following an incomplete C4 (fourth cervical
vertebrae) level spinal cord injury, a resulting symptom is almost
complete loss of biceps muscle strength. Initial stages of
rehabilitation simply involve the patient lifting their arm, in a
repetitive fashion, with the assistance of a physical therapist.
Once the patient has progressed far enough to lift their arm
themselves, they can re-learn how to feed and care for themselves.
A conventional robot-aided therapy merely provides the same
repetitive lifting of the arm, but with a robot and without the
therapist. Still, the patient must progress far enough to lift
their arm themselves before leaving the hospital.
[0008] It will be appreciated that the patients described above
have not lost a limb. Rather, the patients have lost strength in
one or more limbs or body parts. Other types of injury, for which a
patient has lost limb, are treated with prosthetic devices which
replace the lost limb.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, a powered orthotic
device that is worn by and physically controlled by a patient
suffering from neurological trauma, spinal cord or other nerve
damage including stroke or neuromuscular disorder (e.g. muscular
dystrophy, myotonias, myopathies or other congenital disorders) or
a patient requiring general rehabilitation services or strength
increase includes a brace to be couple to a desired body part, a
sensor which senses an electrical signal at a muscle which is
usually proximate the body part and an actuator coupled to receive
a signal from the sensor and to provide a force having a magnitude
which is proportional to a magnitude of the sensor signal. The
sensor senses or otherwise determines a desired joint torque and
the actuator applies a proportional amount of torque in parallel
with the torque provided from the patient's own muscle. The sensor
may include an integrated processor which utilizes signals produced
by the sensor or alternatively the processor may be separate from
the sensor. With this particular arrangement, a patient-worn which
device provides the patient with an ability to control the limb or
body part affected by spinal cord or other nerve or muscular damage
more rapidly than previous therapy methods is provided. Since the
powered orthotic device allows the patient to control an affected
body part, the patient is able to more rapidly leave a hospital or
other institution. Also, in cases where full rehabilitation is not
possible, the patient can continue to use the powered orthotic
device to perform activities of daily living. Also for patients
with spasticity and tremor, it is possible to filter or extract the
meaningful information from the user and reject the "noise"
associated with the user's input, enabling them to smoothly move a
spastic limb or body part. For patients that suffer from
co-contraction it is possible to have the weaker, patient
controllable, muscle group overpower the stronger, uncontrollable
opposing muscle. Thus, in general the orthotic device could discern
a patient's intent, despite co-contractions. The powered orthotic
device of the present invention thus corresponds to a wearable,
unencumbering exoskeleton that augments human physical capability
by working in parallel with existing musculature. The device of the
present invention both augments strength and can accelerate
rehabilitation in people who have suffered from neurological trauma
or neuromuscular disorders, or a general loss of strength.
[0010] In accordance with the present invention, a powered orthotic
device for augmenting a person's muscular functionality includes a
brace to be coupled to a body part of a person, about a joint. The
brace includes at least one elastic brace strap for attaching the
brace to the body part. An electromyographic (EMG) sensor is fixed
within an elastic strap such that the sensor is coupled to at least
one muscle of the person. In response to the person attempting to
move the body part, the sensor senses a surface EMG signal of the
muscle or muscles connected to the joint. The powered orthotic
device determines a desired joint torque from the EMG signal, and
provides a control signal in response thereto. An actuator is
coupled to receive the control signal, and in response to the
control signal, the actuator provides a force having a magnitude
which is proportional to a magnitude of the control signal. The
ratio of power delivered by the actuator to the mass upon which the
actuator acts is selected such that the body part moves in a
desired manner (e.g. in a smooth, controlled manner). When
considering the mass upon which the actuator acts, it is necessary
to take into account all of the elements contributing to the mass.
In some embodiments in which the actuator is supported by the
orthotic device and the user, the mass of the actuator itself
should be considered.
[0011] In accordance with another aspect of the present invention.,
the powered orthotic device described above also includes a control
means coupled to the actuator. The control means includes means for
making a measurement of the joint torque and means for providing a
feedback signal to the actuator to ensure an accurate application
of the force provided by the actuator.
[0012] With this particular arrangement, the powered orthotic
device can be controlled by a patient having spinal cord or other
nerve damage, including stroke, by way of the EMG signal generated
by the patient, to bend or otherwise move a joint or body part
which the patient is otherwise unable to effectively move. In this
way, the patient can be quickly rehabilitated to use their limb or
body part, or can use the powered orthotic device for daily
activities where rehabilitation is not fully possible.
[0013] In one embodiment, a wearable, powered, orthotic device that
provides external assistance to enable a user to move in a desired
motion is provided. The powered orthotic device provides increased
strength for victims of degenerative neuromuscular conditions as
well as other conditions. The device is worn by a user (e.g. in the
form of a sleeve or a brace-type structure) and includes sensors
which sense an electromyogram (EMG) signal generated by flexor and
extensor muscles of a joint. The signals are processed to determine
the user's desired joint torque and that information is provided to
a control system. The control system adds a proportional amount of
assistance to the riser via a force provided to the user's limbs,
for example, by a relatively light weight, actuator. This approach
provides a relatively compact, inexpensive system. In some
embodiments, all components of the system (including the actuator
and power supply) are worn by the user. In this case, the device is
fully portable. In such a fully portable embodiment, it may be
preferable to provide the power supply as a relatively lightweight
power supply. Relatively high mass components of the device can be
mounted on the brace or a portion of the user's body in manner
which does not impede the user's ability to move. Alternatively
still, in another fully portable embodiment, relatively heavy
components of the system (e.g. the actuator and power supply) may
be worn by the user in a hip pack or other support structure. Such
a support structure is preferably coupled to the user to support at
least some components of the orthotic device while still keeping
the orthotic device fully portable. At the same time, the support
structure is provided so as not to add any additional mass (or a
resistive force) to the limb or other body part to which the
orthotic device is providing assistance. In other embodiments, an
external power supply (e.g. the power supply from a wheelchair or
other external device) can be used in which case portability
depends upon the portability of the external power supply.
Likewise, an actuator which is physically supported by an external
structure other than the orthotic device or by the user (e.g. a
wheelchair) can also be used. Again, in this case portability
depends upon the portability of the external actuator.
[0014] By providing a device which is lightweight, portable, and
wearable able, the device enables the wearer to carry on routine
activities such as eating, personal hygiene, or controlling a
wheelchair. One benefit is that the user will be able to use, and
potentially retrain affected limbs following incidents such as
stroke, incomplete spinal cord injuries, etc. The device also
allows rehabilitation to be accomplished through the execution of
daily tasks, decreasing the need for lengthy therapy sessions which
are costly in terms in terms of effort, money and human
resources.
[0015] In one embodiment device, portability and wearability are
accomplished via a compact, high power density, high force actuator
used with a lightweight structural brace. The actuator can be
provided as an electric actuator, a hydraulic actuator, a pneumatic
actuator of some combination thereof. In one embodiment, the device
determines intended muscular force via surface electromyagram (EMG)
sensors, force sensors, position sensors, velocity sensors or some
combination thereof. A force estimator determines desired joint
torque from the sensor signal. An output of the estimator can be
scaled by a variable amount and an active feedback loop controls
the amount of force applied to the joint by the actuator. Thus, the
force exerted by the externally worn brace can be selected such
that it is proportional to a function of the magnitude of the
sensor signals. In one embodiment, the feedback loop relies on a
relatively low impedance measurement of output torque to ensure an
accurate application of force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The foregoing features of the invention, as well as the
invention itself may be more fully understood from the following
detailed description of the drawings, in which:
[0017] FIG. 1 is a diagrammatic view of a powered orthotic
device;
[0018] FIG. 2 is a block diagram of a powered orthotic device
having a force feedback path;
[0019] FIG. 3 is a (graph slowing a measured electromyographic
(EMG) signal;
[0020] FIG. 4 is a graph shoving a processed EMG signal and a
resulting measured toque provided a powered orthotic device,
and
[0021] FIG. 5 is a diagrammatic view of a powered orthotic device
worn by a user in a wheelchair.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to FIG. 1, an exemplary powered orthotic device 10
is used by a patient who has lost the ability to normally bend an
elbow, leg or other jointed body part is shown. It should be
understood that although the powered orthotic device 10 is shown in
FIG. 1 applied to an arm, the device (or a suitably adapted
variant) can be used with a leg or other jointed body part.
[0023] In the embodiment shown in FIG. 1, a first attachment strap
or cuff 12 can be worn on the forearm of the patient and a second
attachment strap or cuff 18 can be worn about the biceps arm region
of the patient. In one particular embodiment, the first and second
straps 12, 18, respectively, can be elastic straps and can include
fasteners (not shown), for example, hook and loop type fasteners,
buttons, hooks, etc., which can allow the patient or caregiver to
fasten and unfasten install and remove the first and second straps
14, 18 at will to facilitate wearing and removal of the device. In
other embodiments, a zipper, buckle or friction-type strap
attachment could be used. In still other embodiments, one or both
of the attachment straps 12, 18 may be provided from an open or
closed cell foam (e.g. a neoprene sleeve) having either an external
or integrated hinge (i.e. a hinge mechanism integrated on, under or
within the sleeve). In the case where an attachment strap is
provided as a sleeve, a sensor can be placed under the sleeve. Such
a sleeve would provide the function of holding the sensor in place
while also holding other elements of the device 10 onto the
body.
[0024] It should also be appreciated that one attachment device
(e.g. an elastic strap) could be provided to attach the device 10
to a body while a different attachment device that was not used to
attach the device to the body was used to hold sensors against the
body. In this case, the device 10 would have an attachment portion
(which may have an elastic characteristic) and would thus hold
itself onto the body while a separate strap (also possibly having
an elastic characteristic) would hold sensors in appropriate
locations proximate or against a user wearing the orthotic
device.
[0025] The patient wears the first and second straps 12, 18,
respectively, about their elbow, the first strap 12 below their
elbow, and the second strap 18 above their elbow, about their
bicep.
[0026] In one particular embodiment, the first and second straps
12, 18 are coupled with a hinge mechanism 14 having first and
second hinge portions 14a, 14b, respectively, which allow the first
and second straps 12, 18 to move relative to each other in
accordance with normal movement of the patient's elbow. In some
embodiments, the hinge mechanism 14 can include adjustable physical
stops or locks (not shown) which can limit the range of movement of
the first strap 12 relative to the second strap 18 in order to
avoid potential injury to the patient. The first and second straps
12, 18 together with the hinge mechanism 14, are herein referred to
as a brace 40. In some embodiments, the person's joint may serve as
the hinge, eliminating the necessity of a hinge mechanism on the
brace.
[0027] A cable wheel 20 has a groove 22 adapted to receive a
continuous cable 26. The continuous cable 26 passes around the
cable wheel 20 within the groove 22. The continuous cable 26 is
retained on the second strap 18 by a cable retainer 30. It will be
appreciated that when the cable 26 is moved, the cable wheel 20
rotates, causing the first and second straps 12, 18 to move
relative to each other in an angular motion resembling a bending
elbow. The cable 26 can have an inner cable portion 26a, which,
along certain portions of the cable 26, is surrounded by an outer
cable jacket 26b, through which the inner cable portion 26a can
slide. The cable 26 is received by an actuator 36 having force
feedback control, which provides the movement of the cable 26. A
power source 38, for example a battery, provides electrical power
to the actuator 36. In one embodiment, the power source may
correspond to the power source of a wheel chair in which the
patient sits. The power source may be provided solely for the
purpose of providing power to the orthotic device 10 or
alternatively, the power source may be used to provide power to the
orthotic device 10 as well as to other devices (e.g. the wheelchair
drive system).
[0028] A pair of sensors 32a, 32b, collectively 32, are disposed to
sense signals generated by a person wearing the orthotic device 10.
In the exemplary embodiment shown in FIG. 1, the sensors 32 are
provided as surface EMG sensors and thus it is important to have
good contact between the sensor and the skin of the patient's body.
To that end, the sensors 32 are coupled to an inner surface 18a of
the second strap 18 so as to be in contact with a patienit's skin
against a biceps muscle, and/or against a triceps muscle, when the
second strap 18 is worn by the patient.
[0029] It should be appreciated that in one embodiment, the sensors
32 are separate from the straps 12, 18 while in another embodiment,
the sensors are coupled to or even provided as an integral part of
the straps 12, 18. For example, the sensors may be fixed to a
surface of the strap or the sensors may be integrated within the
strap material. Alternatively, the sensors 32 can be attached
directly to the body (e.g. by glue, other adhesive), or just held
on by a strap (e.g. one of the cuffs 12, 18) without being fixed in
it (i.e. the sensor can be held onto the body by contact force
between the strap and the sensor and the body).
[0030] In one particular embodiment, the sensors 32 are provided as
non-invasive electromyographic (EMG) sensors. Utilizing EMG sensors
having relatively stiff electrodes (or more particularly relatively
stiff electrode contact pads) contributes to the occurrence of
artifacts due to motion of the person wearing the brace (referred
to as "motion artifacts"). One reason motion artifacts occur is
because relatively stiff electrode contact pads do not bend as a
body part (e.g. an arm or leg) changes shape during motion. The
occurrence of such motion artifacts can be reduced by wrapping, an
element having an elastic characteristic around the relatively
stiff surface EMG electrodes. In one exemplary embodiment, this is
accomplished by wrapping a sleeve or sleeve-type structure provided
from a closed cell foam (e.g. neoprene) or other material having
similar elasticity and strength characteristics around the
electrode and wrapping the sleeve-electrode combination around a
body part (e.g. an arm). By using, a stiff but elastic element
wrapped around relatively stiff surface EMG electrodes, the
electrodes are less likely to disconnect from the surface of the
skin of a person wearing the device which would result in an
erroneous reading. The EMG sensors can be provided having built in
amplifiers and filters. The above approach helps prevent both
partial and full disconnects of electrodes/electrode pads.
[0031] In other embodiments, the sensors 32 may be provided as
invasive electromyographic (EMG) sensors. In still other
embodiments, the sensors 32 may be provided as a type of sensor
other than an EMG sensor. In other embodiments, one or more of the
sensors 32 may be provided as force sensors or another device that
senses muscular contraction by determining change in radius of the
limb, stiffness of the surface of the limb or the force which the
limb exerts against an inside surface of the brace. In some
applications, it may be desirable for the sensors 32 to receive
input signals in addition to (or in some cases, in place of) EMG
signals. For example, sensors which measure or sense joint angle,
velocity or other parameters may be used in addition to (or in some
applications in place of) EMG sensors. Such additional input may be
desirable to provided additional functionality including but not
limited to higher quality desired torque estimates, safer
operation, application to a wider range of conditions, which may be
desirable for treating certain conditions or certain types of
patients such as stroke patients, for example.
[0032] The sensors can also be provided to measure signals from
muscles not connected to the joint about which the device 10 is
disposed. For example, the sensor could be disposed such that an
action of flexing the left bicep muscle sends a signal to move the
right elbow.
[0033] In summary, the sensors 32 may be provided as any type of
invasive or non-invasive sensor capable of sensing information of
the type required to allow appropriate control signals to be
provided to a control system 36 to be described below. The
particular type of sensor to select for use in a particular
application depends upon a variety of factors including but not
limited to the type of signal which must be detected, the
characteristics of the signal to be detected, the reliability of
the sensors, sensitivity of the sensors and cost of the sensors,
the location on the body at which the sensors are placed, the
proximity relative to the body at which the sensors must be placed,
the size of the sensors, the available area on the body at which to
place the sensors, the strength of an output signal provided by the
sensors and the conditions of the environment in which the sensors
will operate.
[0034] The sensors 32a, 32b are coupled to a processor 34 adapted
to run control software. It should be appreciated that one or more
of the sensors may be provided as wireless sensors which transmit
sensor signals to the processor 34. In this case, the processor is
adapted to receive wireless signal transmissions from the sensors.
Alternatively, one or more of the sensors may be coupled to the
processor via a conventional wired signal path.
[0035] The processor 34 may implement a control algorithm which
produces a control signal which represents a force which is not
directly proportional to the sensor signal. For example, it may be
desirable to utilize a control methodology which takes into account
non-linearities such as saturation (force limits).
[0036] The processor 34 may also implement a pre-programmed series
of motions, either in response to one or more user inputs (e.g.
signals sensed by the sensors 32) or independent of sensor signals.
For example, if the user wants to keep their arm in its current
position for an extended period of time (say, while drinking from a
cup), they flex their arm quickly two times.
[0037] Load sensor or force sensor 16 (also referred to herein as a
load cell or a joint torque sensor), adapted to sense tension upon
the cable 26 (which is proportional to torque about the hinge
assembly 14), is coupled to the actuator 36, forming a feedback
loop. Optionally, the sensor 16 is coupled to the processor 34,
also forming a feedback loop to the actuator 36. Sensor 16 may be
selected such that it senses one or a variety of different forces
including but not limited to tension, compression and torque.
[0038] A joint position sensor 24, coupled to the hinge assembly,
is adapted to sense position of the hinge assembly 16 and to
provide a rotation signal to processor 34. One of ordinary skill in
the art will recognize that the joint position sensor 24 can be one
of a variety of conventional rotation sensors and the tension
sensor 16 can be one of a variety of conventional tension sensors.
In the case where the orthotic device 10 does not include a hinge
assembly (e.g. the person's joint itself functions as a hinge), the
joint position sensor 24 can be disposed directly on the person's
joint to sense or measure the position of the person's joint (or
the position of limbs disposed on either side of the joint) and to
provide a rotation signal to the processor 34. The joint position
sensor can also be placed on the output shaft of the actuator if
there is a known correlation between the movement of the actuator
and joint.
[0039] The processor 34 is coupled to the actuator 36, controlling
operation or the actuator 36, and therefore, relative motion of the
first and second straps 12, 18, respectively. A power source, for
example, a battery, provides power to the actuator 36. The actuator
is selected having operating characteristics which are desirable
for the particular application in which the orthotic device will be
used. The particular type of actuator to select for use in a
particular application thus depends upon a variety of factors
including but not limited to the type of application, the
reliability of the actuator, the sensitivity of the actuator, the
cost of the actuator, the location at which the actuator will be
placed (e.g. will the actuator be supported by the user in a fully
portable system or supported by external means such as a
wheelchair), the proximity relative to the body at which the
actuator must be placed, the size of the actuator, the available
area on the body at which to place the actuator, the strength of an
output provided by the actuator and the conditions of the
environment in which the actuator will operate.
[0040] In operation, when the patient attempts to move a body part
(e.g. when the patient attempts to move their arm as shown in FIG.
1), signals (e.g. EMG signals) (generated by the patient's muscles
are sensed by the sensors 32a, 32b (e.g. EMG sensors). The signals
are sent to the processor 34 which controls the actuator 36. In
response to the signals the actuator moves the inner portion 28a of
the cable 28, which moves the first strap 12 relative to the second
strap 14. In the embodiment shown in FIG. 1 in which the orthotic
device is disposed on an elbow, this causes the patient's arm to
bend about their elbow. In this way, a patient having signals
having a relatively small amplitude (e.g. EMG signals having a
relatively small amplitude), in the vicinity of their biceps and/or
triceps muscles, can still bend their elbow in response to the
small EMG signal, with the assistance of the powered orthotic
device 10. This operation is able to occur even when the signals
measured from the patient are of insufficient strength (or
frequency) to activate the patient's biceps and/or triceps muscles
to move their arm. The above-described method of operation applies,
of course, to any jointed body region (e.g. wrist, legs, ankles,
etc . . . ).
[0041] The amount of power delivered by the actuator 36 to the mass
upon which the actuator 36 acts, takes into account all of the mass
which must be moved by the force. In some embodiments, the mass of
the actuator itself is considered in determining the necessary
amount of power. For example, if the actuator is mounted on the
brace itself, at a more distal location than the joint upon which
it acts, then it is necessary to consider the mass of the actuator
in determining the necessary amount of power needed for desired
operation of the device.
[0042] In one particular embodiment, the actuator 36 comprises a
motor adapted to move the cable 26. While an actuator mechanism
comprising the cable wheel 20, the cable 26, the cable retainer 30,
the actuator 36, and the power source 38 is shown, it should be
understood that other actuator mechanisms can be used with this
invention. For example, in another embodiment, an actuator (not
shown), for example, a servo motor, stepper motor, hydraulic or
pneumatic motor, can be coupled directly to the hinge mechanism 14,
between the first and second portions 14a, 14b, without use of the
cable 26. In yet another embodiment, a hydraulic actuator mechanism
can be used and the cable 26 can be replaced with hydraulic lines.
In yet another embodiment, a pneumatic actuator mechanism can be
used and the cable 26 can be replaced with pneumatic lines. Also,
in other embodiments, it is possible to provide an actuator
mechanism which merely moves the first and second straps 12, 18 in
one direction in accordance with a bending elbow, and passive
springs or the like can move the first and second straps 12, 18 in
accordance with a straightening elbow, or vice versa. It should
also be understood that the actuator may be provided as a lineal or
a non-linear actuator.
[0043] It should also be understood that in one embodiment, the
device 10 can be provided such that the actuator is physically
located on the device while in another embodiment the actuator is
not physically located on the device.
[0044] In one particular embodiment, the processor 34, the actuator
36, and the power source 38 can be coupled to a wheelchair, while
the brace portion 40 is not attached to the wheelchair. This makes
the powered orthotic device 10 lightweight and filly portable with
the wheelchair. In another embodiment, the processor 34, the
actuator 36, and the power source 38 can be coupled to a stationary
rehabilitation centers along with the other parts of the powered
orthotic device 10, and the patient can come to the rehabilitation
center for therapy from time to time.
[0045] While two sensors 32a, 32b are shown, it should be
appreciated that fewer than two or more than two sensors can be
used. Also, while the sensors are shown to be coupled to the inner
surface 18a of the second strap, in other embodiments, one or more
sensors can be coupled to an inner surface 12a of the first strap
12, in place of or in addition to the sensors 32a, 32b. Also,
although the sensors 32 are sometimes described herein as
non-invasive EMG sensors, as described above, it should also be
appreciated that sensors other than EMG sensors could also be used.
For example, position, velocity and force transducers may be used
in addition to or even in place of the EMG sensors. Furthermore,
invasive sensors (e.g. needle-type EMG sensors) may be used in
place of the non-invasive sensors (e.g. in place of surface EMG
sensors).
[0046] By appropriate selection of materials and components from
which the orthotic device is provided, a wearable, affordable,
unencumbering exoskeleton that augments human physical capability
by working in parallel with existing musculature is provided. Also
the device can be made lightweight by appropriate selection of the
brace materials. Also by selecting non-invasive sensors, the device
itself is non-invasive.
[0047] It should be appreciated that although the device has been
described above as a powered orthotic device for augmenting a
person's muscular functionality, it should also be understood that
the device can also be used for exercise, by working against the
user's muscular force. As easily as the system can assist or
augment a person's muscular functionality, the device could also be
made to provide resistance by negating the control signal to the
actuator. Thus, in this application, instead of providing an
external force that is proportional and in the same direction as a
person's muscular force, the device could provide a force that
would be proportional and in an opposing direction to a person's
muscular force. In other embodiments, the device could provide
resistance to user motion that is not necessarily proportional to
the sensor signals (for example, a brace that resists motion based
on speed, or position, or the trajectory history of the user).
[0048] It should also be appreciated that the brace portion of the
device may be provided in the form of a splint or a sleeve or other
structure rather than a conventional brace-type structure. For
example, in some embodiments, straps 12 and 18 may provide the
brace. Thus, the orthotic device can be provided as a device which
utilizes sensors (e.g. EMG sensors to sense signals used to provide
control signals), which is constructed from new components (rather
than being a modification of a preexisting brace) and which
provides a proportional force in parallel (or against) a person's
muscular force.
[0049] It should also be appreciated that in some embodiments, the
portions of the device which attach to a person's body (e.g. straps
12, 18 in FIG. 1) are provided such that the device traverses at
least one joint of the person. In some applications, however, it
may be desirable to provide a device which spans two or more
joints. For example, the device may span from above the shoulder
all the way to the wrist, with at least one assistive actuator
disposed proximate each joint. It should also be understood that
the device may be provided such that it attaches to the body above
and below a joint, but does not actually cover the joint. This is
illustrated in FIG. 1, for example, by an embodiment in which the
hinge 14 is omitted from the brace, leaving essentially cuffs 12,
18 around the upper and lower parts of the arm, with a pull cable
between them and the natural elbow acting as a pivot).
[0050] It should also be understood that the device can also be
adapted for use with animals (rather than humans).
[0051] The brace can also be constructed such that it attaches to
more than one part of the body (e.g. shoulder, elbow and wrist) and
it can also be provided such that it moves without significant
input from the wearer. The brace can also be provided such that it
moves upon some signal other than the person attempting to move.
For example, in some applications, it may be desirable to provide a
brace which moves in response to a person flexing a muscle. That
is, a rather than trying to move a body part, a person could simply
toy to flex a muscle and in response to the flex action, the brace
would apply force and cause motion.
[0052] In one particular embodiment, the device 10 determines a
desired joint torque from an EMG signal measured by an EMG sensor.
It should be appreciated, however, that the orthotic device 10
could also determine joint torque from an input other than an EMG
signal. For example position, velocity, force, torque, time-history
of trajectories (i.e. applying torque based on how active, or how
the user has been moving the limb over the past 5 minutes . . . ),
vibration (frequency of tremors) could all be used to provide the
control signals.
[0053] While the description above describes the device such that
in response to a sensor signal the actuator provides a force having
a magnitude which is proportional to a magnitude of the sensor
signal, it is not necessary for the device to operate in this
manner. For example, in one embodiment, it may be desirable to
provide a brace/actuator combination that acts without input from
the sensors. For example, a spring return could be included on the
triceps side of device shown in FIG. 1.
[0054] Referring now to FIG. 2, a powered orthotic device 50
includes a brace 52 which is worn by a user. The brace 52 may, for
example, be provided as the attachment cuffs 12, 18 or other
structures described above in conjunction with FIG. 1. And, in the
case where a person's joint or body part does not serve the
function, the brace may optionally include the hinge mechanism 14
of FIG. 1.
[0055] A sensor system 54 includes sensors 54a-54c disposed on or
proximate to the wearer of the brace 52 senses muscle movement or
other characteristics of the brace wearer and provides signals to a
torque estimator processor 56. In this exemplar embodiment, three
sensors are shown with a first sensor 54a corresponding to an EMG
sensors a second sensor 54b corresponding to a joint position
sensor and a third sensor 54c corresponding to a joint torque
sensor which measures joint torque. Other types of sensors such as
those described above in conjunction with FIG. 1 may also be
used.
[0056] Also, although three sensors are shown in FIG. 2, it should
be appreciated that as few as one sensor could be used.
Alternatively, an unlimited number of sensors could be used. Thus,
in some applications it may be desirable or even necessary to use
as few as one sensor while in other applications, it may be
desirable or even necessary to use a plurality of sensors. The
particular number of sensors to use in any application may be
selected in accordance with a variety of factors including but not
limited to cost, amount of space available to mount the sensors,
the type of input which is being measured on the wearer, activity
level of the user, the limb on which the brace is being worn, the
thickness of skin and fat covering the user's muscles, number of
muscles being monitored, type of condition the brace is being used
to treat.
[0057] As indicated by the dashed lines in FIG. 2, one or more of
the sensors may optionally be attached to the brace 52. In such
embodiments, the brace helps couple one or more of the sensors
54a-54c to the wearer of the brace 52. It should be noted, however,
that it is not necessary for the sensor to be coupled to the brace
52.
[0058] A torque estimator processor 56 receives the signals
provided thereto from the sensor system 54 and processes the sensor
signals to produce an estimate of the desired joint torque. The
joint torque processor 56 then provides a joint torque estimate
signal to an actuator controller 58.
[0059] The actuator controller 58 receives the signal from the
torque estimator 56 and provides a control signal to an actuator
and drive train assembly 60. The torque estimator processor
provides a low power control signal, while the actuator controller
outputs a high power driving signal to the actuator.
[0060] The actuator and drive train assembly 60 are coupled to the
brace 52 being worn by the patient. The actuator and drive train
assembly 60 may, for example, include the cable 26, the cable
retainer 30, and the cable wheel 20 of FIG. 1. The actuator
controller 58 and the actuator and drive train 60 may also include
a combination of motors and force feedback control circuits. It
should be appreciated that the processor 65, controller 58 and
actuator/drive train 60 cooperate such that the actuator/drive
train 60 provides to the user an applied force in a smooth and
well-controlled manner. That is, the system components are selected
having operating characteristics and are coupled in a manner which
allows the system to achieve the desired effect of allowing the
system to assist a user to move a desired body part in a controlled
manner with a relatively smooth motion. That is, the system is
provided having a compliance property (i.e. a property reciprocal
to stiffness) which promotes smooth motion of a body part in a
user. This effect is achieved by having the components of the
system operating on various inputs to the system (as described
above) until the output (which is a measure of the desired
effect--e.g. smoothness of the motion or a characteristic of the
actuator output signal) falls within an acceptable range of values.
In one embodiment, a low backlash actuator and drivetrain (both
designed in compliance), as well as compliance inherent in the
system (e.g. by virtue of the coupling mechanisms used to couple
moving components of the system) aid in smoothing out motions
induced by the actuator. Force control, as opposed to pure position
control, is also conducive to smooth motion, as compliance can be a
part of the control process algorithm.
[0061] It should be appreciated that in the exemplary system of
FIG. 2, three control loops are shown. A first control loop is
associated with the surface EMG sensor 54a, a second control loop
is associated with the joint position sensor 54b, and a third
control loop is associated with the joint torque sensor 54c.
[0062] The joint torque sensor 54c can be coupled to the actuator
controller 58, which includes force feedback control circuitry.
Optionally, the joint torque sensor 54c can be coupled only to the
processor 56 or optionally still the joint torque sensor 54c can be
coupled only to the actuator controller 58.
[0063] It will be understood that a control loop is generally
characterized by a variety of parameters, including, but not
limited to, bandwidth and gain. It would be desirable to provide
gains associated with the control loops that can be adjusted in
accordance with a particular patient. This is because each patient
has spinal cord or other nerve damage that results in different
magnitude EMG signals sensed by the powered orthotic device 50.
Therefore, the processor 56 and/or the force feedback control of
the actuator controller 58 can be provided with adjustable gain.
The adjustable gain can be provided in a variety of ways, including
but not limited to variable analog gain in the form of an
adjustment knob or switches, and variable digital gain in the form
of programmable firmware or switches. The particular gain and
bandwidth selected to use in any particular application are
selected in accordance with the details of the application.
[0064] It is generally desirable to filter analog sensor signals
before they are converted to the digital domain for processing. In
this way, signal to noise ratio can be improved and alias products
generated in the digitization process can be minimized. Therefore,
is desirable to provide filters to filter signals provided by the
joint torque sensor 16, the joint position sensor 24, and the
surface EMG sensor 32. The particular filter characteristics
selected to use in any particular application are selected in
accordance with the details of the application. It should be
appreciated that the specific characteristics of the filters used
in ally application will vary widely based upon a variety of
different factors including, but not limited to, the condition that
is being treated, the physiology of the user and the type of use of
the device (rehabilitation vs. activities of daily living).
[0065] It should be appreciated that the above described filtering
and processing functions may be implemented in either in software
or hardware or by using a combination of both software and hardware
distributed between the sensor system 54 and the actuator 60.
[0066] In a practical case, the force feedback loop could be
incorporated into a filtering and processing element, so the
command signal provided to the actuator 60 is actually the command
signal from the force feedback control loop.
[0067] It should also be appreciated that there is not necessarily
a direct link between the sensors of the sensor system 54 and the
actuator and drive train 60. All information can be passed through
the processor 56 and controller 58. This means that the actuator 60
responds to commands from the processor 56 and controller 56, which
are based upon the signals from the sensor system 54, but the exact
relationship (linear, non-linear, twitch control, saturation
limits, etc) between the output signal provided by the actuator
controller 58 (i.e. actuator command signal) and the output of the
sensors (e.g. sensors 54a-54c) is unspecified because it will vary
from treatment to treatment, patient to patient, etc . . .
[0068] Referring now to FIG. 3, a measured EMG sensor signal 72 is
provided by EMG sensors, for example, the EMG sensors 32 of FIGS. 1
and 2. The EMG sensor signal is shown on a graph 70 having an
x-axis in units of milliseconds and a y-axis in units of volts.
[0069] The EMG sensor signal 72 was measured on the biceps of a
patient having spinal cord damage and who is unable to lift their
forearm. Even though the patient was not able to lift the weight of
their own forearm, the EMG signal 72 has sufficient amplitude and a
good signal to noise ratio. In addition, the repeatability of the
EMG signal 72 was good, suggesting that the patient has a good
degree of control over the small EMG signal 72, even though they
lack strength.
[0070] The same experiment carried out on patients with varying
levels of spinal cord injury (C3-C7), in addition to one patient
with ALS (amyotrophic lateral sclerosis, a degenerative
neurological disorder) has shown good results and
repeatability.
[0071] Referring now to FIG. 4, a graph 100 includes an x-axis in
units of milliseconds and a y-axis in units of volts. A first curve
102 corresponds to a processed EMG signal, for example a processed
version of the EMG signal 72 of FIG. 3. In one particular
embodiment, the processing includes pre-filtering, rectifying, and
low pass filtering the EMG signal to provide the processed EMG
signal 102 as an amplitude envelope of the EMG signal 72. However,
in other embodiments, other processing can be performed upon the
EMG signal 72 to provide the processed EMG signal 102.
[0072] A curve 104 corresponds to a resulting torque applied to the
powered orthotic device, as measured by a force transducer, for
example the tension sensor 16 of FIG. 1. It can be seen that the
shape of the curve 102 is similar to the shape of the curve 104,
differing primarily in amplitude. When scaled to be of the same
amplitude, it can be shown that the curve 102 differs from the
curve 104 only by about one percent. Thus, the powered orthotic
device achieves a torque 104 corresponding to the EMG signal 72
generated by the patient.
[0073] Referring now to FIG. 5, an orthotic device 110 is disposed
on a user 112. The device 110 is also coupled to a wheelchair 114
in which the user 112 is seated. The device includes sleeves or
cuffs 116a, 116b, 116c disposed on an arm of the user 112. The
cuffs 114a-114c are coupled via connecting structures 116a, 116b
and joint structures 115a, 118b. The cuffs 114a-114c, connecting
structures 116a, 116b and joint structures 118a, 118b together from
an exoskeleton worn by the user 112.
[0074] An actuator 120 is coupled to the exoskeleton via cables
disposed in a housing 122 while the weight of the actuator is
supported by the wheelchair 114. By using cable drives and stiff
but somewhat elastic cable housings, it is possible to position
relatively heavy portions of the device 110 (e.g. the actuator and
power supply) in locations in which the mass has a relatively small
impact upon the magnitude of the forces which the actuator must
provide to assist the user 112.
[0075] While the larger mass points of the system (e.g. the
actuator and the power supply) are shown in FIG. 5 to be supported
by an external structure (e.g. the wheelchair), it should be
appreciated, that such relatively large mass points may also be
worn by the user in a hip pack or other support structure attached
to and supported by the user's body. Such support structures are
preferably coupled to the user to support at least some components
of the orthotic device while still keeping the orthotic device
fully portable. At the same time, the support structure should
preferably be provided so as not to add any additional mass (or a
resistive force) to the limb or other body part to which the
orthotic device is providing assistance in such a manner that
substantially negatively impacts the user's ability to move the
limb. It should be understood that a portion of the brace itself or
the user's body itself may act as the support structure. That is
the relatively high mass points may be mounted directly on the
brace itself or the user's body itself. Also, the drive system can
be provided to allow convenient placement of the larger mass points
(e.g. a power supply or actuator) in a hip pack or other support
structure.
[0076] While the powered orthotic device has been shown and
described in conjunction with a first and second strap 12, 18 (FIG.
1) worn about a patient's elbow, it should be appreciated that a
similar powered orthotic device can be worn about any of the
patient's movable joints or body parts to assist movement of those
joints or body parts in response to EMG signals measured about
those joints or body parts.
[0077] All references cited herein are hereby incorporated herein
by reference in their entirety.
[0078] Having described preferred embodiments of the invention it
will now become apparent to one of ordinary skill in the art that
other embodiments incorporating their concepts may be used. It is
felt therefore that these embodiments should not be limited to
disclosed embodiments, but rather should be limited only by the
spirit and scope of the appended claims.
* * * * *